To date, there are no production logging sensors capable of measuring downhole gases (such as H2, O2, CO2, CH4, C2H6, H2S). However, knowledge of these species within a reservoir fluid would aid in deciding which, if any, downhole zones should be isolated; deciding on which materials should be used for pipelines and, in the case of H2S, provide a means of knowing where a scavenger should be injected and how much scavenger is required.